I have some interesting/strange wheelweights......

[Harry O]

I bought a couple of hundred pounds of truck sized wheelweights a few years ago. They have a characteristic that I did not see with car sized wheelweights that I had used for years before (I don't used car WW anymore for several reasons -- zinc being the major one). I normally add tin in the neighborhood of 2% to 3% to the WW when casting bullets.

Anyway, I melted down the truck WW, cleaned out the steel and impurities, and cast them into ingots. They were about Bhn 11-12 at the time of casting. I checked the ingots again after a year or so and found them to be Bhn 15-16. I thought this was very strange. The car sized WW's I had used before did not change hardness after casting. The bullets I have cast from these ingots display a behavior similar to the ingots. Since then I have been doing some testing.

The bullets are air dropped into a dry towel and allowed to cool normally. When tested for hardness immediately after the casting is done, the hardness is Bhn 12-13 (after the addition of tin). They do not harden very fast. It will take from two months to as much as four months for the bullets to get to Bhn 15-16.

I also tried quenching the bullets in water and get Bhn 22-25 in about a week or two, which is fairly normal behavior. Obviously, the WW's have some arsenic to allow them to get harder when quenched, but how does that work with air-dropped bullets? Any ideas?

[HangFireW8]

Measuring hardness immediately after casting is kind of pointless. My usual measuring data points are taking at 3 days, 2 weeks, and 3 months (if they last that long). For most alloys, 3 months is barely harder than 2 weeks, and 2 weeks is about 1-2 BHN harder than 3 days.

I suspect you have a lead/tin/antimony alloy. It takes about 3 months for enough of the crystallization to occur and the combination of these three can make for a harder alloy at lower percentages than binary alloys. Dennis Marshall wrote a good article about this, can't seem to hunt it up right now.

I once had a small bucket of truck wheel weights, I smelted it separately and it came out around 15-16BHN, one of my hardest WW batches ever without additional alloying. I'd buy more in a heartbeat.

HF

[runfiverun]

yes the truck weights have more antimony in them.
it takes some time for a cast object to settle down to it's final bhn.
give the air cooled castings about two weeks and they will be close to normalized.
i like to give water dropped alloys as long as i can before using them.
but a month at the minimum.
this allows all of the castings a chance to "normalize"